1. Field of the Invention
The present invention relates to an antenna device to be contained in a communication apparatus such as a radio or the like, and a communication apparatus containing the antenna
2. Description of the Related Art
The inventors have proposed an antenna device as shown in FIG. 23 in Japanese Patent Application No. H10-295350. It should be noted that the proposed example shown in FIG. 23 does not constitute the related art of the present invention.
In an antenna device 1 shown in FIG. 23A, a patch type radiation electrode 3 and a microstrip type radiation electrode 4 are formed on the surface of a dielectric substrate 2. The antenna device can transmit and receive radio waves in different frequency bands as shown in the return loss characteristic diagram of FIG. 23B.
In particular, as shown in FIG. 23A, on the rectangular parallelepiped dielectric substrate 2, the patch type radiation electrode 3 is formed, and also, the microstrip type radiation electrode 4 is formed thereon at a predetermined interval between the electrodes 3 and 4. Moreover, on a side face 2b of the dielectric substrate 2, a feeding electrode 5 is formed in the vicinity of the patch type radiation electrode 3, and also, the microstrip radiation electrode 4 is formed so as to elongate from the upper face 2a, bend, and elongate toward the feeding electrode 5 along the upper side of the side face 2b to form a feeding end 4a. The feeding end 4a of the microstrip type radiation electrode 4 is positioned at a predetermined interval between the end 4a and the feeding electrode 5. Furthermore, in this example, fixing electrodes 6 to fix the antenna device 1 to a mounting substrate are formed at the corners on the under-face side of the side face 2b of the dielectric substrate 2.
Furthermore, the feeding electrode 5 is formed so as to elongate from the side face 2b and bend onto the under face 2f. A ground electrode 7 is formed substantially on the whole of the under face 2f of the dielectric substrate 2 excluding the area in which the feeding electrode 5 is formed and at an interval between the electrodes 5 and 7.
Moreover, the microstrip type radiation electrode 4 is formed so as to elongate from the upper face 2a toward the under face 2f via a side face 2d, and is connected to the ground electrode 7 on the under face 2f. That is, the top 4b of the elongated microstrip type radiation electrode 4 forms a ground short-circuited end which is connected to the ground electrode 7.
The patch type radiation electrode 3 is a xc2xd patch type, and is not connected to the ground (in other words, the electrode is separated from the ground), and resonates at a resonance frequency f1 as shown in FIG. 23B. Moreover, the microstrip type radiation electrode 4 is a xc2xc microstrip type, and resonates at a resonance frequency f2 which is lower than the above-mentioned resonance frequency f1, as shown in FIG. 23B.
The antenna device 1 is mounted onto a mounting substrate contained in a communication apparatus, with the under face 2f of the dielectric substrate 2 being used as a mounting surface. On the mounting substrate (not shown), a signal supply 8 is provided. When the antenna device 1 is plane-mounted in a predetermined area on the mounting substrate, the feeding electrode 5 is connected to the signal supply 8.
When a predetermined power (signal) is supplied from the signal supply 8 to the feeding electrode 5, the signal is fed from the feeding electrode 5 to the patch type radiation electrode 3 and the microstrip type radiation electrode 4 through capacitive coupling. Based on the signal, the patch type radiation electrode 3 and the microstrip type radiation electrode 4 resonate. Thus, transmission-reception of a radio wave (signal) is carried out.
The microstrip type radiation electrode 4 is short-circuited to the ground electrode 7. Accordingly, the microstrip type radiation electrode 4 is equivalent to the ground electrode 7 with respect to the patch type radiation electrode 3. In many cases, a radio wave radiated from the patch type radiation electrode 3 is desired to have a symmetrical directivity. The directivity of the patch type radiation electrode 3, however, is unbalanced, since the microstrip type radiation electrode 4 equivalent to the ground is formed in one of the right and left sides (in the right side in the example of FIG. 23A) of the patch type radiation electrode 3, as described above. That is, the directivity of the patch type radiation electrode 3 is unsymmetrical.
In view of the forgoing, the present invention has been devised. It is an object of the present invention to provide an antenna device and an antenna each of which contains both of the patch type radiation electrode and the microstrip type radiation electrode, and the directivity of the patch type radiation electrode exhibits a good symmetry.
To achieve the above object, the present invention, having the following constitution, provides a means for solving the above problems.
An antenna device in accordance with the present invention includes an antenna device comprising a dielectric substrate, a patch type radiation electrode separated from ground and formed on the surface of the dielectric substrate, and first and second microstrip type radiation electrodes formed on both sides of the patch type radiation electrode at predetermined intervals between the first and second microstrip type radiation electrodes and the patch type radiation electrode, and short-circuited to the ground.
According to the present invention, transmission-reception of radio waves in at least two different frequency bands can be performed by means of only one antenna device, since the antenna device contains the patch type radiation electrode and the two microstrip type radiation electrodes. Moreover, since the first and second microstrip type radiation electrodes are formed on both sides of the patch type radiation electrode at predetermined intervals between them, the microstrip type radiation electrodes equivalent to the ground have effects on both sides of the patch type radiation electrode substantially to the same degree. Thus, a good symmetry of the directivity of the patch type radiation electrode can be attained.
Preferably, the first and second microstrip type radiation electrodes are arranged substantially symmetrically with respect to the patch type radiation electrode. In this case, the symmetry of the patch type radiation electrode can be further enhanced.
Also preferably, the first and second microstrip type radiation electrodes have different resonance frequencies. In this case, the frequency band of the first and second microstrip type radiation electrodes can be widened by decreasing the difference between the resonance frequencies of the first and second microstrip type radiation electrodes to produce a double resonance state.
Moreover, by increasing the difference between the resonance frequencies of the microstrip type radiation electrodes, frequency band of the first microstrip type radiation electrode, and a frequency band of the second microstrip type radiation electrode different from that of the first microstrip type radiation electrode are produced, in addition to the frequency band of the patch type radiation electrode. Accordingly, transmission-reception of radio waves in the three different frequency bands can be performed. Thus, a multiple functions can be provided to the antenna device.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.